The invention relates to a method for controlling a state of charge of a vehicle battery for the purpose of ensuring the startability of the vehicle.
The startability of vehicles depends fundamentally on various status factors of the starter battery. One significant status factor is the temperature of the battery when the vehicle is started. The lower the battery temperature, the higher the state of charge of the battery has to be in order to be able to guarantee starting of the vehicle. In order to be able to ensure startability, attempts are currently being made to estimate, via a risk assessment, the lowest battery temperature that might obtain when the vehicle is started. For the purpose of estimating the lowest temperature, the lowest temperature during the parking time of the vehicle and the lowest temperature during travel are ascertained and are drawn upon as a so-called “worst case” for the risk assessment. Depending on this estimated lowest battery temperature, a lower state-of-charge limit of the vehicle battery is determined, and the amount of charge in the vehicle battery is controlled in such a way that the state of charge of the battery at least does not fall below the lower state-of-charge limit. A future evolution of the temperature is not taken into account in this case.
A method for controlling a state of charge of a vehicle battery is already known from DE 10 2012 001 820 A1, wherein a battery-temperature prediction for the vehicle battery is generated. This battery-temperature prediction is used in order to determine a desired (temperature-dependent) SOC range for the vehicle battery. For the purpose of generating the battery-temperature prediction, inter alia a forecast outside temperature at the current position of the vehicle is received by a telematics terminal which receives this forecast temperature from a weather service.
A disadvantage in this case is that even when, on the basis of the telematics data, very low temperatures are forecast which would require an adaptation of the SOC range, the state of charge of the battery at the relevant parking location can no longer be increased to a sufficient extent, since the vehicle will shortly be parked or has already been parked.
Now, the object of the invention is to provide a method for controlling a state of charge of a vehicle battery, said method being improved as regards the aforementioned problems.
This and other objects are achieved by a method for controlling a state of charge of a vehicle battery for the purpose of ensuring the startability of the vehicle, wherein a battery-temperature prediction for the vehicle battery is ascertained and the battery-temperature prediction is used in order to determine a lower state-of-charge limit of the vehicle battery. The amount of charge in the vehicle battery is controlled such that the state of charge of the battery at least does not fall below the lower state-of-charge limit. Data of a navigation system integrated within the vehicle or coupled with the vehicle are taken into account in the ascertainment of the battery-temperature prediction.
The method according to the invention and also advantageous configurations thereof can be carried out by means of an implemented algorithm or by means of an appropriate arrangement of assemblies in a control unit provided for this purpose.
The method according to the invention for controlling a state of charge of a vehicle battery for the purpose of ensuring the startability of the vehicle is basically configured in such a manner that a battery-temperature prediction for the vehicle battery is ascertained and this battery-temperature prediction is used in order to determine a lower state-of-charge limit of the vehicle battery. The amount of charge in the vehicle battery is consequently controlled in such a way that the state of charge of the battery at least does not fall below the lower state-of-charge limit.
Now the insight underlying the invention is that although in the case of the method known from DE 10 2012 001 820 A1, a future (regarded temporally) battery-temperature prediction on the basis of known meteorological data is undertaken at the current position of the vehicle, under certain circumstances falling temperatures can then be reacted to only very late—in some cases too late. This may have the consequence that the startability can no longer be ensured, since an appropriate charging of the battery is no longer possible because the vehicle is no longer in operation (has not been in operation long enough).
In order to obviate this problem, the method according to the invention provides that data of a navigation system integrated within the vehicle or coupled with the vehicle are taken into account in the ascertainment of the battery-temperature prediction. Said data are advantageously data that include or make possible a statement about the future position of the vehicle. These data can make a relevant contribution to the outcome that a battery-temperature prediction is already undertaken in good time in regions in which ensuring the startability of the battery is relevant.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.